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What is the radiation balance? How does it determine the temperature on Earth?

Solar radiation consists of visible light, ultraviolet radiation and infrared radiation. A part of this sunlight is reflected by:

  • clouds
  • Earth’s surface (particularly snow and ice)
  • atmospheric aerosols, which are microscopic particles suspended in the atmosphere

The reflected part of the solar radiation is called “albedo”. The remaining sunlight heats the Earth. The Earth reflects this energy as infrared radiation.

A part of this earth radiation is absorbed by atmospheric gases, the so-called greenhouse effect. Without this greenhouse effect, Earth would be about 30°C colder because the heat in the earth system would escape back into space at a faster rate.

Changes in the atmospheric composition can influence climate

By altering the amount of infrared earth radiation absorbed by the atmosphere:
Human activity increases the concentration of gases like CO2, methane and ozone that can absorb infrared radiation. This enhances the “greenhouse effect” and results into global warming.

It has been suggested that the surface of the Earth has warmed up 0.5°C since the beginning of the 20th century. In the future global warming would even rise more.

By changing the amount of sunlight reflected into space:
Human activity releases many gases (like SO2) that are converted into atmospheric aerosols. These particles sometimes scatter and absorb a part of the sunlight. In addition, some aerosols play a key role in the formation of clouds.

An increased concentration of aerosols causes clouds to glitter more. In this way, clouds reflect even more sunlight. Aerosols therefore reduce the amount of sunlight on the Earth’s surface, causing the climate to cool down and compensating the warming effect. This explains why the temperature rise on Earth is less felt in the utterly polluted northern hemisphere than in the southern hemisphere.